Bone grafting is a technique used to repair or help in the healing of osseous damage caused by procedures and pathologies such as surgery, tumors, trauma, congenital deformities, implant revisions, and joint fusions. The two most common methods presently used to restore bone are allografting and autografting.
Allografting, which comprises transplantation of tissue from a donor into a host subject, has both clinical and practical drawbacks. Clinically, allografting exposes the host subject to a risk of acquiring an infection and/or other disease such as a host immune system-mediated antigraft response. Practical problems with this procedure are that donor tissue is often expensive or unavailable.
Autografting, which comprises the transplantation of autologous tissue from one site in a subject's body to another, suffers fewer problems as compared to allografting. For example, because the host and donor are the same subject, the risk of infection and immune system-mediated rejection are significantly reduced. However, autografting is still disadvantageous in that it requires that two separate surgical procedures (one to harvest the tissue; one to transplant the tissue) to be performed on the subject. Additionally, the supply of usable autologous bone is limited because it is collected from only one subject.
To avoid problems associated with allografting and autografting, synthetic bone-grafting materials have been developed. Synthetic bone-grafting materials offer numerous clinical and practical advantages. The clinical advantages include (1) reduced risk of infection and/or rejection and (2) no complications from tissue harvesting surgery. Practical advantages of using synthetic materials include the possible selection of materials that exhibit superior mechanical properties, materials which can be fashioned into custom-made shapes and sizes, and materials which can be made in large quantities.
A number of different compositions have been used as synthetic materials for bone grafting. Predominant among these are calcium phosphates such as hydroxyapatite. Hydroxyapatite, the main mineral component in bone, is the most stable calcium phosphate form under normal physiological conditions. It is a particularly good material for use in bone grafting because it readily bonds with bone, and is biocompatible and osteoinductive, permitting bone repair in a location that would not normally heal if left untreated. Used alone, however, hydroxyapatite lacks mechanical strength and cannot withstand substantial stress.